1. Field of the Invention
The present invention relates to a method for curing organosiloxane compositions to form a silicone rubber. More specifically, the present invention relates to a novel method for curing organosiloxane compositions which use an organohydrogenpolysiloxane as the curing agent in the absence of a curing catalyst or an organoperoxide.
2. Description of the Prior Art
Known methods for curing organosiloxane to form a silicone rubber include (1) the condensation of silanol substituted organopolysiloxanes with organosilicon compounds having a plurality of hydrolyzable groups, for example. alkoxysilanes, acetoxysilanes or aminoxysilanes; (2) the free radical initiated polymerization of diorganopolysiloxanes in the presence of organoperoxides; and (3) a hydrosilylation reaction between compounds containing silicon-bonded hydrogen atoms and organopolysiloxanes containing ethylenically unsaturated hydrocarbon radicals, for example, silicon-bonded vinyl radicals, in the presence of a platinum catalyst.
The necessity for using platinum metal or a platinum compound to catalyze curing of organpolysiloxanes by a hydrosilation reaction is taught in the literature, including a text entitled "Chemistry and Technology of Silicones" by Walter Noll, published as an English translation in 1968 by Academic Press, New York: and an article entitled "Silicone Elastomer Developments 1967-1977" by E. L. Warrick et al. [Rubber Chemistry and Technology, 52 (3), 1979].
Recently disclosed methods for curing organosiloxane compositions include curing by means of ultraviolet irradiation; curing by means of high-frequency radiation, infrared radiation or electron beams and the polymerization of mercapto substituted diorganopolysiloxanes in the presence of organoperoxides. Of these known methods, curing in the presence of organoperoxides and curing via a platinum catalyzed hydrosilylation reaction are the ones most generally used. Curing of organosiloxane compositions using organoperoxides suffers from the problem of organoperoxide decomposition residues remaining in the cured product, with the result that the product requires post-vulcanization to remove or inactivate these residues.
The disadvantages associated with curing by a hydrosilation reaction are poor storage stability and short use time of the curable organosiloxane composition.
To avoid these problems, the present inventors examined various methods for curing organosiloxane compositions with the objective of providing a novel method for curing these compositions without the need for a curing catalyst or an organoperoxide.